Some recipes I see for bread dough recommend a short rest between the mixing (just enough to make the ingredients homogeneous) and kneading stage - often 10 to 30 minutes. The dough seems to be a little easier to work after the rest, but what is going on there in such a short time?
Besides the initial gluten relaxing that mrwienerdog wrote about, another important effect is the absorption of liquid.
It takes time for the flour to fully hydrate with the available liquid. Before it does the dough will be more sticky and there will be less gluten available for kneading. Giving the recently incorporated dough a short rest allows the flour to pull in all the liquid it can and become much easier to work with.
A similar effect can be seen with pastry doughs. Even though often the goal is to minimize gluten development, a short rest gives the flour time to hydrate and can turn pastry dough from difficult to work and crumbly to soft and smooth.
You give the gluten a chance to relax. If you work a bread too soon, the gluten tears. You should always allow your doughs to rest between makeup stages, for this very reason. Of course, if you are careful, you can skip it. However, as you mentioned, the dough will be far more 'bucky' (as my old instructor called it) and harder to work.